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Rising sea levels create ‘ghost forests’ on US coast | Climate change

Trekking on my research sites near North Carolina Alligator River National Wildlife RefugeI glide knee-deep in the water on a completely submerged section of trail. Permanent flooding has become commonplace on this lower peninsula, tucked away behind the Outer Banks of North Carolina. Trees that grow in water are small and stunted. Many have died.

All over the coast of North Carolina, evidence of the disappearance of forests is omnipresent. Almost all of the roadside ditches I cross as I travel the area are lined with dead or dying trees.

As ecologist studying the response of wetlands to sea level riseI know these floods prove that climate change is altering landscapes along the Atlantic coast. It is emblematic of environmental changes that also threaten local wildlife, ecosystems, farms and forest businesses.

Like all living organisms, trees die. But what is happening here is not normal. Large patches of trees die simultaneously and saplings do not sprout to take their place. And that’s not just a local problem: seawater increases salt levels in coastal forests along the entire Atlantic Coastal Plain, from Maine to Florida. Vast swathes of contiguous forest are dying. They are now known in the scientific community as “ghost forests”.

The insidious role of salt

The sea level rises driven by climate change makes wetlands more humid in many parts of the world. It also makes them more salty.

In 2016, I started working in a wooded wetland in North Carolina to study the effect of salt on its plants and soils. Every two months, I wear heavy rubber waders and a mesh shirt to protect myself from biting insects, and I haul over 100 lbs of salt and other gear along the flooded trail to my research site. . We lounge an area the size of a tennis court, seeking to mimic the effects of rising sea levels.

After two years of effort, the salt didn’t seem to affect the plants or soil processes we were monitoring. I realized that instead of waiting for our experimental salt to slowly kill these trees, the question I had to answer was how many trees were already dead and how many more wetlands were vulnerable. To find answers, I had to go to sites where the trees were already dead.

Rising seas flood the coast of North Carolina and salt water seeps into the wetland soils. Salts move through groundwater during phases of freshwater depletion, such as during droughts. Salt water also moves through canals and ditches, penetrating inland with the help of wind and high tides. Dead trees with pale trunks, devoid of leaves and limbs, are a telltale sign of high levels of salt in the soil. A 2019 report called them “wooden tombstones“.

As the trees die off, more salt tolerant shrubs and grasses move to take their place. In a recently published study with which I co-authored Emily bernhardt and Justin wright at Duke University and Xi Yang at the University of Virginia we show that in North Carolina this change was dramatic.

The coastal region of the state has suffered a rapid and widespread loss of forests, with cascading effects on wildlife, including endangered species. Red wolf and Red cockade pick. Wetland forests sequester and store large amounts of carbonThe disappearance of forests therefore also contributes to further climate change.

Evaluating ghost forests from space

To understand where and how fast these forests are changing, I needed a bird’s-eye perspective. This perspective comes from satellites like NASA Earth Observation System, which are important sources of scientific and environmental data.

Since 1972, Landsat satellites, operated jointly by NASA and the US Geological Survey, captured continuous images of the Earth’s land surface which reveal both natural and human-induced changes. We have used Landsat imagery to quantify changes in coastal vegetation since 1984 and referenced high-resolution Google Earth images to locate ghost forests. Computer analysis identified similar patches of dead trees throughout the landscape.

The results were shocking. We have found that over 10% of the forested wetlands in the Alligator River National Wildlife Refuge have been lost in the past 35 years. This is federally protected land with no other human activity that could kill the forest.

Rapid rise in sea level seems to exceed the capacity of these forests to adapt to wetter and saltier conditions. Extreme weather events, fueled by climate change, are causing further damage from severe storms, more frequent hurricanes and drought.

We found that the largest annual loss of forest cover in our study area occurred in 2012, following a period of extreme drought, forest fires and storm surges. Hurricane Irene in August 2011. This triple whammy appears to have been a tipping point that caused massive tree deaths in the region.

Should scientists fight the transition or help it?

As global sea level continues to rise, coastal forests Gulf of Mexico at chesapeake bay and elsewhere in the world could also suffer significant losses of salt water intrusion. Many members of the conservation community are rethinking approaches to land management and exploring further adaptive strategies, such as facilitating the inevitable transition from forests to salt marshes or other coastal landscapes.

For example, in North Carolina Nature conservation implements adaptive management approaches, such as the creation of “living shores”Made from plants, sand and rock to provide natural protection against storm surges.

A more drastic approach would be to introduce salt tolerant marsh plants into threatened areas. This strategy is controversial because it goes against the will to try to preserve ecosystems exactly as they are.

But if the forests die anyway, having a salt marsh is a much better result than allowing a wetland to be reduced to open water. While open water isn’t inherently bad, it doesn’t provide the many ecological benefits that a salt marsh does. Proactive management can extend the life of coastal wetlands, allowing them to continue to store carbon, provide habitat, improve water quality, and protect productive agricultural and forest lands in coastal regions.

  • Emily Ury is a PhD candidate in Ecology at Duke University

  • This article is republished from the conversation, a non-profit news organization dedicated to sharing ideas from academic experts

Rising sea levels create ‘ghost forests’ on US coast | Climate change

Source link Rising sea levels create ‘ghost forests’ on US coast | Climate change

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